Ye Linzheng, Zhu Xijing
Modern Processing Theory and Technology Research Institute, School of Mechanical and Power Engineering, North University of China, Taiyuan 030051, China.
Modern Processing Theory and Technology Research Institute, School of Mechanical and Power Engineering, North University of China, Taiyuan 030051, China.
Ultrason Sonochem. 2017 May;36:507-516. doi: 10.1016/j.ultsonch.2016.12.030. Epub 2016 Dec 24.
The bubble collapse near a wall will generate strong micro-jet in a liquid environment under ultrasonic field. To explore the effect of the impact of near-wall acoustic bubble collapse micro-jet on an aluminum 1060 sheet, the cavitation threshold formula and micro-jet velocity formula were first proposed. Then the Johnson-Cook rate correlation material constitutive model was considered, and a three-dimensional fluid-solid coupling model of micro-jet impact on a wall was established and analyzed. Finally, to validate the model, ultrasonic cavitation test and inversion analysis based on the theory of spherical indentation test were conducted. The results show that cavitation occurs significantly in the liquid under ultrasonic field, as the applied ultrasonic pressure amplitude is much larger than liquid cavitation threshold. Micro pits appear on the material surface under the impact of micro-jet. Pit depth is determined by both micro-jet velocity and micro-jet diameter, and increases with their increase. Pit diameter is mainly related to the micro-jet diameter and d/d≈0.95-1.2, while pit's diameter-to-depth ratio is mainly negatively correlated with the micro-jet velocity. Wall pressure distribution is mostly symmetric and its maximum appears on the edge of micro-jet impingement. Obviously, the greater the micro-jet velocity is, the greater the wall pressure is. Micro pits formed after the impact of micro-jet on aluminum 1060 surface were assessed by ultrasonic cavitation test. Inversion analysis results indicate that equivalent stress, equivalent strain of the pit and impact strength, and velocity of the micro-jet are closely related with pit's diameter-to-depth ratio. For the pit's diameter-to-depth ratio of 16-68, the corresponding micro-jet velocity calculated is 310-370m/s.
在超声场作用下，靠近壁面的气泡坍塌会在液体环境中产生强烈的微射流。为了探究近壁声空化气泡坍塌微射流对1060铝板的冲击效果，首先提出了空化阈值公式和微射流速度公式。然后考虑了Johnson-Cook率相关材料本构模型，建立并分析了微射流冲击壁面的三维流固耦合模型。最后，为验证该模型，进行了超声空化试验以及基于球形压痕试验理论的反演分析。结果表明，在超声场作用下，液体中会显著发生空化现象，因为施加的超声压力幅值远大于液体空化阈值。在微射流冲击作用下，材料表面出现微坑。坑深由微射流速度和微射流直径共同决定，并随它们的增大而增加。坑直径主要与微射流直径有关，且d/d≈0.95 - 1.2，而坑的径深比主要与微射流速度呈负相关。壁面压力分布大多是对称的，其最大值出现在微射流冲击边缘。显然，微射流速度越大，壁面压力越大。通过超声空化试验对微射流冲击1060铝表面后形成的微坑进行了评估。反演分析结果表明，坑的等效应力、等效应变、冲击强度以及微射流速度与坑的径深比密切相关。对于径深比为16 - 68的坑，计算得到的相应微射流速度为310 - 370m/s。
